1. Field of the Invention
The present invention relates to methods for preparing amides, and more particularly, to a method using a catalyst composition for preparing an amide.
2. Description of the Prior Art
Caprolactam is an important raw material in the manufacture of nylon 6 fibers and thin films. Beckman rearrangement of cyclohexanone oxime is an important reaction step in producing caprolactam. Currently, oleum is used as a catalyst for converting cyclohexanone oxime to caprolactam sulfate during Beckman rearrangement, and then ammonia is used for neutralization, so as to obtain caprolactam. While the conversion rate of cyclohexanone oxime is almost 100% and the selectivity for caprolactam is 99%, a large amount of low-valued ammonium sulfate is generated during the reaction, and concentrated sulfuric acid used for catalysis causes problems such as corrosion to the whole equipment and environmental pollution. In recent years, researches on new production technologies of caprolactam focus on reducing or avoiding the generation of the by-product, ammonium sulfate. U.S. Pat. No. 6,265,574 discloses subjecting cyclohexanone oxime to a gaseous phase Beckmann rearrangement reaction in a fluidized bed system, wherein there is no byproduct, ammonium sulfate, produced in the gaseous conversion reaction, but selectivity of caprolactam is only 95.7%, and the reaction temperature (300-350° C.) is higher than that of liquid phase reaction. In addition, the major disadvantage of the gaseous conversion reaction is that the catalyst is easily inactive, and thus the regeneration of the catalyst is frequently required, which is disadvantageous to the long term continuous operation.
U.S. Pat. No. 3,912,721 and U.S. Pat. No. 3,904,609 disclose the extraction of amides in an acid and the subsequent purification, wherein caprolactam is recovered by an extraction agent to a specific group. However, during the extraction of amides, water needs to be added to oleum, and it is hard to remove the water during the process. If sulfuric acid contains too much water, cyclohexanone oxime would be hydrolyzed in the conversion reaction to form cyclohexanone, and thus the selectivity is significantly reduced. Therefore, oleum in such method cannot be regenerated.
Hence, there is a need to develop a liquid phase rearrangement of a ketoxime for preparing an amide, wherein the method has a high conversion rate of a ketoxime, a high selectivity of an amide and regeneration of a catalyst.